Papers by Keyword: Crack Control

Abstract: Ceramics is a material of hardness and brittle, so crack arises easily when it is machined. To improve its cutting performance and enhance machining quality, a dynamic model based on constant-shearing-stress is built for milling ceramics, therefore some cutting parameters can be optimized by the model for no crack machining; moreover, an algorithm of 5 axis tool-path designed with constant-shearing-stress is put forward. According to the model and the algorithm, 5 axis tool paths of decreasing-cutting-depth and decreasing-feed-rate are realized; these are really accurate and smooth through VERICUT software simulating. Using Mikron high-speed machining center, several experiments were done to find a good method of crack control in milling thin-wall ceramics. The results show that the experiment based on the 5 axis tool paths with high pressure air cooling and regional cutting is rather successful because of no cracking in cutting thin-wall ceramics, compared to others.

Abstract: With the continuous development of the level of China's political, economic and social, the construction industry also obtained great progress. At the same time, the quality problems of all kinds of building has become a very serious problem which restricting the expansion of the scale of the enterprise. Along with the global integration, exchanges between domestic and foreign construction companies are becoming more and more frequent. The quality issues is in relation to the future of the construction industry. Only to deal with this problem, we can win in the international competition of the company. In the future for a long period of time, the construction industry will have a greater impact on the national economy of our country. If we can not solve the fundamental problem restricting the development of construction industry, the development of this industry will not sustainable. There is a very serious problem In the course of engineering construction which is the crack control of reinforced concrete structures. If this problem can be solved, we can produce a relatively good effect in the development of China's construction industry.

Abstract: Combined with engineering examples, describes the reasons for the large volume of concrete cracks proposed comprehensive measures to control cracks from all aspects of mass concrete harmful cracks eliminate achieved remarkable results, for the future of similar mass concrete construction provides some guidance .

Abstract: Raft foundation was researched in this paper,basing on the traditional “Wang Tiemeng Method”,the influence of temperature stress calculation by radiation condition was put forward emphatically. According to analysis the two calculation results, obtains the more precise temperature stress calculational method. Consequently the of concrete crack calculation and analysis result can be more precise and reliable.

Abstract: With the development of modern building design and construction technology, high strength concrete technology were getting more use in engineering and more requirements. The authors produced C80 HPC by using Portland cement, blast furnace slag, micro bead and Flyash as cementitious material, have prepared the concrete with grade of C80, low pumping resistance (rewinding time less than 6s), low shrink (72h early self-shrinkage value at 0.028%), high workability (slumps over 240mm and divergence over 700mm) and high durability (diffusion coefficient in concrete after 28d was 1.35×10^-12 m²/s), which would match the requirements of the Guangzhou East Tower.

Abstract: Based on Monte Carlo method, the concrete durability reliability indexes for typical concrete members in 50-year-period of service were calculated under normally moist environment conditions. By taking the typical concrete members under normally moist environment conditions as example, the fuzzy reliability indexes based on durability for crack control criteria provided in GB 50010-2010 were calculated. The calculation results show that the durability reliability indexes are mainly lower than crack control reliability indexes for normally moist environment conditions. To realize the goal that the durability design safety level can be generally closest to crack control safety level, one revision advice was presented for present concrete design code GB 50010-2010 to properly lower the crack control safety level in normally moist environment conditions: the present short period crack width enlargement coefficient should be multiplied with 0.85 so that the calculation guarantee rate will be lowered to 85% for flexural members.

Abstract: The performances of the concrete structure with expansive additives are studied in this research. These expansive additives have helped in reducing the generation of cracks and have showed improved durability. This research evaluates the performance of actual structures through reviews of existing techniques with air permeability, surface water absorption, measurement of distortion of the actual structure and building surveys. The upshot of shrinkage, the significance of restraint and service life in reinforcement is observed in actual structure using concrete with expansive additives. The methods was found that it has a relatively dense surface quality and durability of the concrete structure is said to have endurance level of the planning period.

Abstract: Pile-to-pilecap connection such as in integral abutment bridges is vulnerable to lateral loads as well as seismic loads. This connection may govern the bridge strength and performance against various lateral loads. However, previous researches have merely focused on the connection between pile and pilecap. Preliminary study has investigated possible crack patterns between concrete pilecap and steel HP pile using finite element analyses. It was found that the crack patterns are sensitive to the boundary conditions specified in the simulation. The reinforcement detail specified in PennDOT DM4 was barely effective in controlling crack growing but spiral rebar was proved to be effective in delaying crack growth as well as absorbing energy capacity. In this study, two types of connection details of (1) HSS tube type and (2) removed flange type were investigated in terms of crack control. The connection with a HSS tube exhibited to be effective in prevention of crack propagations from the surface of the bottom pilecap. However, second crack was initiated from the corner region of the tube after first crack was arrested; resulting in lower energy absorption capacity compared to both spiral and removed flange details. In the connection with removed flange, concrete crack initiations were mitigated or delayed successfully.

Abstract: The crack control of the thin-walled high pier for SanBei Bridge is effected by various uncertain factors such as loads, concrete strength and the release of hydration heat etc. Because of the fuzziness for the crack control of thin-walled high pier, it is difficult to accurately calculate the crack width to meet with the requirement of the limiting crack design for the structure. Based on the maximal permit crack formula issued in Concrete Design Specifications, the fuzziness analysis is made to the crack control reliability, the index of fuzzy reliable degrees of the girder maximal permit crack width is calculated by Monte Carlo method, and the sensitivity analysis to uncertain parameters is given to provide reference of the design for SanBei Bridge.

Abstract: Under the action of annual change and sudden drop of air temperature, thermal induced cracking will occur in concrete dam during the operation period. For exploring the temperature control measures for crack prevention, taking a concrete gravity dam section as the research object, sensitivity analyses to the factors which affecting the water-cooling effect are conducted with 3D FEM, some significant suggestions for the water cooling are presented. The results show that, the stresses of the dam surface will decrease to a certain extent after water cooling in the operation period using the cooling water pipe which embedded during construction period, and the cracking risk of the dam will reduce. The study provides a new train of thought for the temperature control and crack prevention of the mass concrete during the operation period.